As computer systems and other types of systems provide increased functionality in smaller form factors, there is a continuing demand for smaller integrated circuit devices. A key factor in determining the size of an integrated circuit device is the package in which an integrated circuit die is provided.
Certain types of integrated circuit device packages have been designed to be small relative to the size of the corresponding integrated circuit die while still providing a relatively large number of input/output terminals. Such packages include ball grid array packages, column grid array packages, and land grid array packages, for example.
Smaller integrated circuit packages that include a large number of input/output terminals can present many challenges for package designers. In particular, designing and routing connections between bondpads on the integrated circuit die and corresponding terminals on a package can be very difficult. The routing must be provided in a small amount of space and must provide for signals communicated via the routing to meet signal quality requirements. Additionally, in some cases, there may be more bondpads on the integrated circuit die than there are terminals on the package.
To illustrate some of the above issues, portions of a ball grid array (BGA) package 100 are shown in FIGS. 1 through 3. Referring first to FIG. 1, a partial top view of a package substrate 101 is shown. An integrated circuit die 105 is mounted to the package substrate 101. A power bus bondring 110, a ground paddle 115 and bondfingers 120 are disposed on the package substrate 101. The ground paddle 115 extends beneath the integrated circuit die 105 to provide multiple ground connections. Conductive traces typically extend from the bondfingers 120 to route signal connections to a corresponding terminal located on an opposite side of the package substrate, but are not shown in FIGS. 1 or 2 for purposes of clarity.
The power bus bondring 110 is provided on the package substrate 101 of FIG. 1 instead of discrete power bondfingers or other types of discrete power connections. The power bondring 110 helps to increase electrical performance of the package 100 by enabling the use of relatively short power bondwires.
Additionally, the power bondring 110 is provided because there may not be enough available terminals for each of several power bondpads on the integrated circuit die 105 (shown in FIG. 3). The power bondring 110 allows a first number of power bondwires to be electrically coupled to the power bondring 110. The power bondring 110, however, is electrically coupled to a smaller number of power terminals on an opposite side of the package substrate.
FIG. 2 shows a partial cross-section of the package substrate 101 and the integrated circuit die 105 taken at the line 2--2. Referring to FIGS. 1 and 2, vias 125 are provided at various points around the power bondring 110 to electrically connect the power bondring 110 to power terminals 205 on an opposite side of the package substrate 101. As shown in FIG. 2, the vias 125 extend through the package substrate 101 to conductive traces or terminal pads 210 that are electrically coupled to corresponding terminals 205. A minimum number of vias 125 corresponding to power terminals 205 may be necessary to ensure that signal quality requirements are met and/or to ensure that power supply or other electrical requirements are met.
FIG. 3 shows a portion of the package substrate 101 and the integrated circuit die 105 in more detail. While the vias 125 are used to connect the power bondring 110 to power terminals 205 on the package substrate 101, they may interfere with power connections from the integrated circuit die 105 to the power bondring 110. As shown in FIG. 3, the integrated circuit die 105 includes bondpads 305. Most of the bondpads 305 are electrically coupled either to the power bondring 110 or to signal bondfingers 120 by corresponding bondwires 310. The bondwires 310 are separated from each other by at least a minimum amount of space to prevent electrical shorts or other issues during encapsulation. The minimum amount of space depends on several factors including the diameter of the wire, and the encapsulation process used.
The bondpads 315 in the example shown in FIG. 3 are power bondpads. The bondpads 315, however, cannot be bonded to the power bondring 110 because of the location of the via 125. Referring to FIGS. 2 and 3, vias such as the via 125 are typically formed by drilling a hole in the package substrate 101 and filling the hole with conductive material. Bonding a bondwire 310 to the via 125 can cause the via 125 to become unstable or loose. As a result, the quality of the power signal and/or the integrity of the package connections may be compromised.
Referring again to FIG. 1, one approach to resolving this issue is to move the vias 125 to other locations along the power bondring 110 in an attempt to avoid having the vias 125 opposite any power bondpads on the integrated circuit die 105. Package designers, however, have little flexibility in terms of where on the power bondring 110 to locate the vias 125. Just as it is undesirable to bond bondwires to vias, it is also undesirable to have a via on one surface of the package substrate directly opposite a power terminal on the opposite side of the package substrate. It is desirable, however, to have the via corresponding to a particular package terminal as close as possible to the package terminal for signal quality purposes. For a package having a dense terminal array, it may be very difficult to avoid having a via directly opposite a corresponding power terminal while still making sure that the power terminal is as close as possible to the corresponding via.
Referring to FIG. 3, another approach to addressing this issue is to relocate the power bondpads on the integrated circuit die 105 to avoid having them opposite the vias. This solution, however, further limits the flexibility of the integrated circuit designer and the package designer in terms of how to bond out the integrated circuit die 105. Specifically, several power connections are typically required for each integrated circuit die and it may not be straightforward to ensure that each of the power bondpads is located in a position on the integrated circuit die such that it is not directly opposite a via. Further, for some cases, a signal bondpad may be rendered unusable if there is not enough room on the package substrate in which to place a corresponding bondfinger due to the placement of the power bondpads.
While a power bus bondring and associated vias on a BGA package are described above, other types of bondrings that include vias on other types of packages may present similar issues when bonding out an integrated circuit die.